If you build it, will they pass? A systematic evaluation of fish passage efficiency for three large-bodied warm-water fishes

Fish passages are constructed to facilitate movement around barriers, but few are quantitatively evaluated for non-salmonids. We quantified the efficiency of a selective, nature-like fish passage for three native fishes, Colorado pikeminnow (Ptychocheilus lucius), flannelmouth sucker (Catostomus latipinnis), and razorback sucker (Xyrauchen texanus), in the San Juan River, NM, USA, by estimating the probabilities of completing three navigational phases and associated delay times. We compared passage efficiency in years when fish were captured in a trap and manually moved upstream to years when the trap was removed in the spring. All species were less efficient at navigating the attraction and exit phases compared with the ascent phase. Operating the passage without the trap generally increased passage success and shortened delay times. The mean probability of passage and delay time among species when the trap was removed ranged from 34%-55% and 5-21 days, respectively. Our results suggest species- and phase-specific variation in passage efficiency and highlight the need for evaluations to aid future passage design and operation for a greater diversity of fish.